All patents, patent applications, and publications cited within this application are incorporated herein by reference to the same extent as if each individual patent, patent application or publication was specifically and individually incorporated by reference.
The invention relates generally to the field of electro-optic polymer waveguide devices. The art of electro-optic polymer waveguide devices and the use of organic second order nonlinear optical polymers in such devices is well documented. A typical electro-optic polymer waveguide, which is illustrated as a cross-sectional view in FIG. 1, is comprised of: 1) an electro-optic polymer core (5); 2) a first polymer clad (10) overlying the electro-optic polymer core (5); 3) a second polymer clad (15) underlying the electro-optic polymer core (5); 4) a top electrode (20) overlying the first polymer clad (10); 5) a bottom electrode (25) underlying the second polymer clad (15); and 6) a substrate (30).
In a typical electro-optic polymer waveguide, the total thickness of the core, first clad, and second clad is around 6-10 μm. Typically, the refractive indices of the polymer clads are chosen to confine a great majority of the optical field in the electro-optic polymer core and keep the optical field from contacting the metal electrodes. The resulting mode in the waveguide is elliptical to such an extent that unacceptably high insertion results when the waveguide is butt-coupled to an optical fiber. The insertion loss can be reduced by using tapers to adjust the size of the fiber mode to the size of the waveguide mode. However, such tapers can be difficult to manufacture.
Making the waveguide mode less elliptical can also reduce insertion loss. A less elliptical waveguide mode can be achieved by decreasing the difference in refractive indices between the clads and electro-optic core. However, such an approach may lead to the optical field contacting one or both of the electrodes, which may cause increased optical loss or complete loss of mode confinement. Such a problem may be overcome by adding lower refractive index clads to act as barriers between the first and second clads and metal electrodes.
U.S. Pat. No. 5,861,976 describes a thermo-optic waveguide having four cladding layers in order to reduce insertion loss while confining the mode away from the silicon substrate and metal heater strip. The first and second “core matching” cladding layers have refractive indices that are 0.0055 lower than the core, while the third and fourth cladding layers have refractive indices that are 0.0215 lower than the first and second cladding layers. The overall device thickness is around 20 μm. The insertion loss of the device is reportedly 2 dB/cm. Although the thermo-optic device showed good (i.e., low) insertion loss, such a device structure applied to electro-optic waveguides would lead to poor power performance since the electrodes are farther away from the electro-optic core than in a typical electro-optic waveguide device; the problem would be compounded since a lesser percentage of light propagates in the core relative to typical electro-optic device structures.